I. Field of the Invention
This invention relates generally to an apparatus and method for fighting fires, and more particularly to a system in which a prescribed quantity of a fire extinguishant in the form of a liquid chemical foamant; is introduced into the main water stream being directed at the fire, such that the resulting foam mixture blankets and smothers the combustible material to limit its exposure to oxygen and to raise the combustion point for that fuel.
II. Discussion of the Prior Art
In combating fires, the application of copious amounts of water to the site is effective to raise the temperature at which combustion takes place. That is, by soaking the combustible materials exposed to the fire with water heat from the fire must first evaporate the water before the temperature of the fuel can be raised to its flash point. In fighting large fires, e.g., forest fires and the like, the application of water alone is oftentimes ineffective because of the size of the area involved and the potential high temperatures encountered. Huge quantities of water must be dropped from aircraft or pumped by ground equipment from lakes and streams if the fire is to be extinguished. This is especially true given the fact that fires often spread subterraneously burning deep in the duff or moss.
Various water additives are now on the market for enhancing the fire extinguishing characteristics of water alone. Specifically, various chemical foamants and surfactants, when added to the water being dumped or sprayed onto the fire scene, creates a foam tending to coat the surface of combustible fuels and deprive them of the oxygen needed for combustion. Moreover, the surfactant, being a wetting agent, permits greater penetration of the treated water into the duff or moss for extinguishing subterraneous fires. When products such as these are applied on fuel, the foaming action allows the mixture to cling to the fuel surfaces, covering it with a layer of material containing more than 99% water. The surfactant action of the additive allows the water to penetrate any oily coatings on the fuel surface which, in turn, permits the water to be absorbed better into the fuel.
Because of cost considerations, it is desirable that the quantity of the surfactant or foamant introduced into the water stream be precisely controlled so as to provide a desired degree of foaming action, but no more. Wormald Canada, Inc. of Ottawa, Ontario, Canada, sells a foamant fire extinguishant under the trademark SILV-EX which it recommends be induced into the water stream so as to comprise 0.7% of flow. Chemical Industries, Inc. of Phoenix, Ariz., sells a concentrate combining foaming and wetting agents under the trademark, FIRE-TROL.RTM. FIREFOAM.TM., which it recommends be applied at 0.2%-0.5% of flow.
In the past, attempts have been made to introduce the chemical foamant into a water stream by using a venturi-type injector. The ability to maintain a desired concentration of chemical in the output stream is difficult because of variations in pressures and flow rates through the venturi and changes in viscosity of the chemical being introduced.
The present invention provides a method and an apparatus for injecting the chemical additive to the water stream in a precise proportion before it is sprayed or dispensed out the end of the fire hose. That is to say, because the system of the present invention includes a computer-based feedback loop which monitors the supply water flow rate and a positive-displacement, adjustable-stroke injector pump whose speed is controlled, the chemical additive is injected at an appropriate rate to maintain a desired concentration in the sprayed mixture. As such, the chemical additive is not needlessly wasted. Also, by utilizing the concentrations recommended by the manufacturers, less damage to the environment results from the application of the fire extinguishant.